1. Technical Field
The invention generally relates to actuators, particularly to electric linear actuators for medical equipments or power seats.
2. Related Art
An electric linear actuator employs a driving unit including a motor, a worm and a worm gear to make a guide screw rotate and to make a telescopic tube screwed on the guide screw linear protrude or retract. Electric linear actuators have been broadly applied in hospital beds, power seats or other fields because of simpler structure and more convenient operation than hydraulic actuators.
To guarantee safety, a conventional linear actuator is always provided with two limit switches separately disposed at two dead centers of a telescopic tube. The limit switches electrically connecting to a motor control the motor to start or stop, so that the telescopic tube will not exceed the predetermined dead centers.
However, the limit switches only work at the two dead centers instead of the whole movement stroke. In other words, the conventional linear actuators do not provide any safety mechanism during the movement stroke except the two dead centers. It is very dangerous to users, especially for children.